Heat exchange catheter with discrete heat exchange elements

ABSTRACT

A catheter for exchanging heat with a body fluid is disclosed. The catheter includes a main shaft and a heat exchange region having a plurality of heat exchange elements each having a length and opposed ends. Each of the elements is attached on at least one of its ends to the shaft and disposed so that when inserted in a fluid body cavity having body fluid therein, the body fluid may circumferentially surround each heat exchange element along a portion of the length of the heat exchange element. The catheter includes a fluid circulation path therein, which desirably includes the hollow lumen within each of heat exchange elements. The heat exchange elements may be connected at two points along the shaft using manifolds that are in fluid communication with fluid flow paths within the shaft. Alternatively, the heat exchange elements may be connected at only one point and be permitted to float in a proximal or distal direction with respect to the catheter. The heat exchange region may be formed on a distal portion of the catheter, or may be formed along the entire length thereof. In the former configuration, an insulating member, such as a balloon, may be provided along the shaft proximal to the heat exchange region. Ribs may be provided on each heat exchange element to disrupt flow therearound and increase heat exchange. Each of the heat exchange elements may be non-circular in cross-section, and may extend in an undulating path with respect to the catheter shaft.

FIELD OF THE INVENTION

This invention relates generally to medical devices and methods and moreparticularly to devices and methods for selectively controlling thetemperature of a patient's body, or portion of the patient's body, byadding or removing heat from the patient's body fluid through the use ofa heat exchange catheter that incorporates a plurality of discrete heatexchange elements in the nature of filaments or tubular members.

BACKGROUND OF THE INVENTION

Under ordinary circumstances, thermoregulatory mechanisms exist in thehealthy human body to maintain the body at a constant temperature ofabout 37° C. (98.6° F.), a condition sometimes referred to asnormothermia. To maintain normothermia, the thermoregulatory mechanismsact so that heat lost to the environment is replaced by the same amountof heat generated by metabolic activity in the body. For variousreasons, a person may develop a body temperature that is below normal, acondition known as hypothermia.

Accidental hypothermia may result when heat loss to the environmentexceeds the body's ability to produce heat internally or when a person'sthermoregulatory ability has been lessened due to injury, illness oranesthesia. Accidental hypothermia is generally a dangerous conditionthat can have serious medical consequences. For example, hypothermia mayinterfere with the ability of the heart to pump blood or the ability ofthe blood to clot normally. Hypothermia may also interfere with varioustemperature sensitive enzymatic reactions in the body with resultantmetabolic and biochemical consequences, and has sometimes beenassociated with impaired immune response and increased incidence ofinfection.

Simple methods for treating hypothermia have been known since very earlytimes. Such methods include wrapping the patient in blankets,administering warm fluids by mouth, and immersing the patient in a warmwater bath. If the hypothermia is not too severe, these methods may beeffective. However, wrapping a patient in a blanket depends on theability of the patient's own body to generate heat to re-warm the body.Administering warm fluids by mouth relies on the patient's ability toswallow, and is limited in the temperature of the liquid consumed, andthe amount of fluid that may be administered in a limited period oftime. Immersing a patient in warm water is often impractical,particularly if the patient is simultaneously undergoing surgery or someother medical procedure.

More recently, hypothermia may be treated by the application of awarming blanket that applies heat to the skin of the patient. Applyingheat to the patient's skin, however, may be ineffective in providingheat to the core of the patient's body. Heat applied to the skin has totransmit through the skin by conduction or radiation which may be slowand inefficient, especially if the patient has a significant layer offat between the warming blanket and the body's core.

Paradoxically, the application of warmth to a hypothermic patient'sskin, whether by immersion in hot water or application of a warmblanket, may actually exacerbate the problem and may even induce shock.The body has certain thermoregulatory responses to cold that work toconserve heat in the body's core, specifically vasoconstriction andarterio-venous shunting (AV shunts). Vasoconstriction occurs when thecapillaries and other blood vessels in the skin and extremitiesconstrict so that most of the blood pumped by the heart circulatesthrough the core rather than through the skin and extremities.Similarly, in AV shunting, naturally occurring blood shunts existbetween some arteries providing blood to capillary beds in the skin andextremities and veins returning blood from those capillary beds. Whenthe body is cooled, those shunts may be opened, allowing blood toby-pass those capillary beds altogether. Thus when the body is cooled,the tissues in the extremities, and particularly at the surface, havelittle blood flowing to them and may become quite cold relative to thebody's core temperature.

When heat is applied to the skin of a hypothermic patient, thetemperature sensors in the skin may cause the vasoconstriction toreverse and the AV shunts to close. When this happens, blood from thecore floods into the very cold tissue on the body surface andextremities, and as a result the blood loses heat to those tissues,often far more than the amount of heat being added by the surfacewarming. As a result, the victim's core temperature may plummet and thepatient may even go into shock.

Partly in response to the inadequacies of surface application of heat,methods have been developed for adding heat to a patient's body byinternal means. A patient being administered breathing gases, forexample a patient under anesthesia, may have the breathing gases warmed.This method may be effective but is limited in the amount of heat thatcan be administered without injuring the lungs. Similarly, a patientreceiving IV fluids may have the fluids warmed, or a bolus of warm fluidmay be administered intravenously. This may be effective in the case ofmild hypothermia, but the temperature of the IV fluid is limited by thetemperature that will be destructive to the blood, generally thought tobe about 41° C.-49° C., and the amount of fluid that is acceptable toadminister to a particular patient.

A more invasive method may be used to add heat to a patient's blood,particularly in the case of heart surgery. Blood is removed from apatient, circulated through a cardiopulmonary by-pass (CPB) system, andreintroduced into the patient's body. The blood may be heated or cooledbefore being reintroduced into the patient. This CPB method is both fastand effective in adding or removing heat from a patient's blood, but hasthe disadvantage of involving a very invasive medical procedure whichrequires the use of complex equipment, a team of highly skilledoperators, and is generally only available in a surgical setting. Italso involves mechanical pumping of blood which is generally verydestructive of the blood tissue resulting in the cytotoxic andthrombolytic problems associated with removal of blood from the body,mechanical pumping of the blood, and channeling the blood throughvarious machines and lines.

Means for adding heat to the core of the body that do not involvepumping the blood with an external, mechanical pump have been suggested.For example, a method of treating hypothermia or hypothermia by means ofa heat exchange catheter placed in the bloodstream of a patient wasdescribed in U.S. Pat. No. 5,486,208 to Ginsburg, the completedisclosure of which is incorporated herein by reference. That patentdiscloses a method of treating or inducing hypothermia by inserting aheat exchange catheter having a heat exchange area including a balloonwith heat exchange fins into the bloodstream of a patient, andcirculating heat exchange fluid through the balloon while the balloon isin contact with the blood to add or remove heat from the bloodstream.(As used herein, a balloon is a structure that is readily inflated underpressure and collapsed under vacuum.) Under certain conditions heat isgenerated within the body or heat is added from the environment inexcess of the body's ability to dissipate heat and a persons develops acondition of abnormally high body temperature, a condition known ashypothermia. Examples of this condition may result from exposure to ahot and humid environment or surroundings, overexertion, or exposure tothe sun while the body's thermoregulatory mechanisms are disabled bydrugs or disease. Additionally, often as a result of injury or disease,a person may establish a set point temperature that is above the normalbody temperature of about 37° C. The set point temperature is thetemperature that the body's thermoregulatory mechanisms actto maintain.Under ordinary circumstances, this is about 37° C. but in other cases,such as fever, the body may establish a different set point temperatureand act to maintain that temperature.

Like hypothermia, hypothermia is a serious condition that may sometimesbe fatal. In particular, hypothermia has been found to beneurodestructive, both in itself or in conjunction with other healthproblems such as stroke, where a body temperature in excess of normal inconjunction with a stroke or traumatic brain injury has been shown toresults in dramatically worse outcome.

As with hypothermia, counter-parts to simple methods for treating thecondition exist, such as cold water baths and cooling blankets, and moreeffective but complex and invasive means such as cooled breathing gasesand blood cooled during CPB also exist. These, however, are subject tothe limitations and complications as described above in connection withhypothermia. In addition, the thermoregulatory responses such asvasoconstriction, AV shunting and shivering, may act directly to combatthe attempt to cool the patient and thereby defeat the effort to treatthe hypothermia. This is especially true in the case of fever, where thebody may establish a set point temperature higher than normothermia andactively resist efforts to reduce the body's feverish temperature tonormothermia.

Although both hypothermia and hypothermia may be harmful and requiretreatment in some case, in other cases hypothermia, and especiallyhypothermia, may be therapeutic or otherwise advantageous, and thereforemay be intentionally induced. For example, periods of cardiac arrest inmyocardial infarction and heart surgery can produce brain damage orother nerve damage. Hypothermia is recognized in the medical communityas an accepted neuroprotectant and therefore a patient is often kept ina state of induced hypothermia during cardiovascular surgery. Likewise,hypothermia is sometimes induced as a neuroprotectant duringneurosurgery.

It is sometimes desirable to induce whole-body or regional hypothermiafor the purpose of treating, or minimizing the adverse effects of,certain neurological diseases or disorders such as head trauma, spinaltrauma and hemorrhagic or ischemic stroke. Additionally, it is sometimesdesirable to induce whole-body or regional hypothermia for the purposeof facilitating or minimizing adverse effects of certain surgical orinterventional procedures such as open heart surgery, aneurysm repairsurgeries, endovascular aneurysm repair procedures, spinal surgeries, orother surgeries where blood flow to the brain, spinal cord or vitalorgans may be interrupted or compromised. Hypothermia has also beenfound to be advantageous to protect cardiac muscle tissue after amyocardial infarct (MI).

Neural tissue such as the brain or spinal cord, is particularly subjectto damage by vascular disease processes including, but not limited toischemic or hemorrhagic stroke, blood deprivation for any reasonincluding cardiac arrest, intracerebral or intracranial hemorrhage orblockage, and head trauma. In each of these instances, damage to braintissue may occur because of brain ischemia, increased intracranialpressure, edema or other processes, often resulting in a loss ofcerebral function and permanent neurological deficits. Although theexact mechanism for neuroprotection is not fully understood, loweringthe brain temperature is believed to effect neuroprotection throughseveral mechanisms including, the blunting of any elevation in theconcentration of neurotransmitters (e.g., glutamate) occurring afterischemic insult, reduction of cerebral metabolic rate, moderation ofintracellular calcium transport/metabolism, prevention ofischemia-induced inhibitions of intracellular protein synthesis and/orreduction of free radical formation as well as other enzymatic cascadesand even genetic responses. Thus intentionally induced hypothermia mayprevent some of the damage to brain or other neurological tissue duringsurgery or as a result of stroke, intracerebral hemorrhage and trauma.

Intentionally inducing hypothermia has generally been attempted byeither surface cooling or by-pass pumping. Surface cooling has generallyproved to be unacceptably slow, since the body heat to be removed mustbe transmitted from the core to the surface, and has sometimes beenaltogether unsuccessful since the body's thermoregulatory mechanisms actto prevent surface cooling from reducing the core temperature of thebody. For example, the vasoconstriction and AV shunting may prevent heatgenerated in the core from being transmitted to the surface by theblood. Thus the surface cooling may only succeed in cooling the skin andsurface tissue, and not succeed in reducing the core temperature of thepatient to induce a hypothermic state.

Another thermoregulatory mechanism that may thwart attempts to reducecore temperature by surface cooling is shivering. There are numeroustemperature sensors on the body's surface, and these may trigger thebody to begin shivering. Shivering results in the generation of asignificant amount of metabolic heat, as much as five times the norm,and with the blood to the surface of the body greatly constricted, thecooling blanket can only reduce the temperature of the patient veryslowly, if at all. If the patient has fever and thus an elevated setpoint temperature, and thus shivers at a temperature above normothermia,it has been found that cooling blankets are often unable to reduce thepatient's temperature even to normothermia.

Additionally, because the heat transfer from the surface to the core ofa patient by the application of cooling blankets is slow andinefficient, the control of the patient's core temperature by surfacecooling is very difficult, if not impossible. The temperature of thepatient tends to “overshoot” the desired low temperature, a potentiallycatastrophic problem when reducing the core temperature of a patient,especially to moderate or sever levels. Speedy adjustment of coretemperature by surface cooling is difficult or even impossible,particularly if precise control is needed.

As is the case with the use of CPB machinery to warm blood removed fromthe body and replace it into the body, by-pass may be fast and controlmay be relatively precise, especially if large volumes of blood arebeing pumped through the system very quickly. However, as was previouslystated, this method is complex, expensive, invasive and generallydamaging to the blood, particularly if continued for any significantperiod of time.

Besides intentionally induced hypothermia or hypothermia, it issometimes desirable to control a patient's temperature to maintain thepatient at normothermia, that is normal body temperature of about 37° C.For example, in a patient under general anesthesia, the body's normalthermoregulatory centers and mechanisms may not be fully functioning,and the anesthesiologist may wish to control the patient's bodytemperature by directly adding or removing heat. Similarly, a patientmay lose an extraordinary amount of heat to the environment, forexample, during major surgery, and the patient's unaided body may not beable to generate sufficient heat to compensate for the heat lost. Thisis especially true where, as a result of the anesthesia used duringsurgery, the patient's normal thermoregulatory response is reduced oreliminated. A device and method for controlling body temperature byadding or removing heat to maintain normothermia, would be desirable.

Additionally, a patient may suffer disease or trauma or have certainsubstances introduced into its body that cause an increased set pointtemperature resulting in fever, as in the case of infection orinflammation. The unaided body may then act to maintain a temperatureabove 37° C. and surface cooling may be ineffective in combating thebody's thermoregulatory activity and reestablishing normothermia. Where,for example in stroke, the presence of fever has been found to correlatewith very negative outcome, it may be very desirable to maintainnormothermia.

The mammalian body generally functions most efficiently at normothermia.Therefore maintaining hypothermia in a portion of the body such as thebrain or heart while maintaining the temperature of the rest of the bodyat normothermia may provide for protection of the target tissue, e.g.neuroprotection of the brain or protection of the myocardium whileallowing the rest of the body to function at normothermia.

For the foregoing reasons, there is a need for a means to add or removeheat from the body of a patient in an effective and efficient manner,while avoiding the inadequacies of surface heat exchange and the dangersof CPB methods that require pumping the blood from the body of thepatient, heating or cooling the blood, and then returning it to thepatient. There is the need for a means of rapidly, efficiently andcontrollably exchanging heat with the blood of a patient so thetemperature of the patient or target tissue within the patient can bealtered, or maintained at some target temperature.

SUMMARY OF THE INVENTION

The present invention provides a heat exchange catheter having a heatexchange portion that comprises multiple heat exchange elements (e.g.,discrete members such as tubes or filaments), and a method of heating orcooling the body of a patient by placing the heat exchange portion ofsuch catheter into the bloodstream of the patient and exchanging heatwith the bloodstream at a sufficient rate and for a sufficient length oftime to alter the temperature of the patient.

Further in accordance with the invention, a heat exchange catheter ofthe invention may comprise a flexible catheter body or shaft having aproximal end and a distal end, the distal end of such catheter shaftbeing adapted to be inserted percutaneously into the vasculature or bodycavity of a mammalian patient. A heat exchange region is provided on thecatheter shaft, comprising a plurality of fluid impermeable heatexchange elements each having a length and opposed ends, each elementbeing attached on at least one of the ends to the catheter shaft. Wheninserted in a blood vessel or other body cavity, body fluid can surroundeach heat exchange element. The shaft of the catheter preferablyincludes a fluid circulation path or lumen, and each heat exchangeelement preferably is attached at both ends to the shaft andincorporates a fluid circulation path or lumen that is in fluidcommunication with the fluid circulation path or lumen of the cathetershaft. In this manner, heat exchange fluid may be circulated into orthrough the individual heat exchange elements as they arecircumferentially surrounded by the body fluid. Alternatively, theindividual heat exchange elements may incorporate cul-de-sac filaments,and may thus be attached to the catheter shaft at only one end.

Further in accordance with some embodiments of the invention, the heatexchange region may be less than one-half the length of the cathetershaft and may be located at or near the distal end thereof. In suchembodiments, an insulating region may be formed on the catheter shaftproximal to the heat exchange region to reduce unwanted transfer of heatto and from the proximal portion of the catheter shaft.

Further in accordance with the present invention, there is provided asystem for heat exchange with a body fluid, the system including a) aliquid heat exchange medium and b) a heat exchange catheter having aplurality of discrete, elongate heat exchange elements. The catheterincludes a shaft having a proximal end and a distal end, the distal endbeing adapted to be inserted percutaneously into a body cavity. Theshaft having a circulation pathway therein for the circulation of heatexchange medium therethrough. The discrete heat exchange elements areattached to the catheter so that when the catheter is inserted in thebody cavity, body fluid surrounds each element.

The system further may include a sensor or sensors attached to orinserted into the patient to provide feedback on the condition of thepatient, for example the patient's temperature. The sensors aredesirably in communication with a controller that controls the heatexchange catheter based on the feedback from the sensors.

Still further in accordance with the present invention, there isprovided a method for exchanging heat with a body fluid of a mammal. Themethod includes the steps of a) providing a catheter that has acirculatory fluid flow path therein and a heat exchange region thereon,such heat exchange region including heat exchange elements that areattached to the catheter shaft at the heat exchange region, b) insertingthe catheter into a body cavity and into contact with a body fluid, theheat exchange elements thus being surrounded by the body fluid and c)causing a heat exchange medium to flow through the circulatory flow pathof the catheter so that the medium exchanges heat with a body fluidthrough the heat exchange elements. Each of the heat exchange elementsmay be hollow, and step C of the method may include causing heatexchange fluid to flow through the hollow heat exchange elements.

It is an object of this invention to provide an effective means foradding heat to a patient suffering from hypothermia.

It is a further object of this invention to provide an effective meansfor removing heat from the bloodstream of a patient suffering fromhypothermia.

It is a further object of this invention to provide an effective meansof adding or removing heat from a patient to induce normothermia.

It is a further object of this invention to provide an effective meansfor maintaining normothermia.

It is a further object of this invention to provide an effective meansof cooling a patient to a target temperature and controllablymaintaining that temperature.

It is a further object of this invention to provide a cooling catheterthat has an advantageous configuration.

It is a further object of this invention to cool a target region of apatient.

It is a further object of this invention to maintain a patient at atarget temperature.

It is a further object of thig invention to provide a heat exchangecatheter that is configured to efficiently exchange heat with the bloodof a patient while allowing continued flow of the blood past thecatheter with a minimum of restriction to that blood flow.

It is a further object of this invention to provide a heat exchangecatheter having multiple heat exchange balloons.

It is a further object of this invention to provide a heat exchangecatheter having a heat exchange portion that comprises multi-filaments.

It is a further object of this invention to provide a heat exchangecatheter having an insulated shaft.

It is a further object of this invention to provide an effective methodof controlling the temperature of a body fluid.

It is a further object of this invention to provide an effective methodof warming a body fluid.

It is a further object of this invention to provide an effective methodof cooling a body fluid.

It is a further object of this invention to provide an effective methodfor inducing hypothermia.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a patient undergoing treatment using asystem in accordance with the present invention;

FIG. 2 is a sectional view of a vessel of a patient showing oneembodiment of a heat exchange catheter of the present invention insertedtherein;

FIG. 3 is an elevational view of an exemplary embodiment of a heatexchange catheter of the present invention having multiple hollowdiscrete elements for flowing heat transfer medium therethrough on adistal portion of the catheter;

FIG. 4A is a sectional view of a proximal end of the catheter of FIG. 3taken along line 4A—4A;

FIG. 4B is a sectional view similar to FIG. 4A of an alternativecatheter;

FIG. 5A is sectional view of the distal heat transfer portion of thecatheter of FIG. 3, taken along line 5—5, and showing six heat exchangeelements.

FIG. 5B is a sectional view, similar to FIG. 5A, of an alternative heattransfer portion of the catheter having three heat exchange elements.

FIG. 6 is a longitudinal sectional view through the distal heat transferportion of the catheter of FIG. 3 taken along line 6—6 of FIG. 5A;

FIG. 7 is a longitudinal sectional view through an alternativeembodiment of a heat exchange catheter of the present invention havingmultiple hollow discrete elements for flowing heat transfer mediumtherethrough disposed along the entire length of the catheter;

FIG. 8 is elevational view of alternative embodiment of a heat exchangecatheter of the present invention having a proximal insulating region,and a distal heat exchange region;

FIG. 8A is a sectional view of an insulating region of the catheter ofFIG. 8, taken along line 8A—8A, with stand-offs interposed between acentral fluid delivery shaft and an outer balloon;

FIG. 8B is a sectional view similar to FIG. 8A of an alternativeconfiguration of an insulating region with a plurality of inflatablespacers between the central fluid delivery shaft and an outer sleeve;

FIG. 9 is an elevational view of a distal portion of an alternativeembodiment of a heat exchange catheter of the present invention having aplurality of flexible heat exchange elements connected at one end to thecatheter;

FIG. 9A is a sectional view of a heat exchange element of the catheterof FIG. 9 having a fluid circulation path therein, taken along line9A—9A;

FIG. 10A is a detailed view of a portion of a discrete heat transferelement of the present invention having a helical fin thereon forenhanced heat transfer;

FIG. 10B is a detailed view of a portion of a discrete heat exchangeelement of the present invention having circumferential fins thereon forenhanced heat transfer;

FIG. 11 is an elevational view of a distal portion of an alternativeheat exchange catheter of the present invention having a plurality ofundulating discrete elements for flowing heat transfer mediumtherethrough;

FIG. 12 is a sectional view through a hollow heat exchange element ofthe present invention having a non-circular configuration and greatersurface area for heat transfer;

FIG. 13 is a sectional view through an alternative heat exchangecatheter of the present intention having a plurality of flexible heatexchange elements connected at one end to the catheter adapted for fluidflow therethrough;

FIG. 14 is a sectional view through one of the flexible heat exchangeelements shown in FIG. 13, taken along line 14—14;

FIG. 15 is a side view of a heat exchange catheter of the inventionhaving coaxial heat exchange elements;

FIG. 16 is a cross-sectional view of the proximal manifold for the heatexchange catheter of FIG. 15;

FIG. 17 is an enlarged cross sectional view of the distal tip of one ofthe coaxial heat exchange elements;

FIG. 18 is a cross sectional view of the proximal shaft portion of theheat exchange catheter taken along line 18—18 of FIG. 15;

FIG. 19 is a plan view of the faceplate of the proximal manifold of theheat exchange catheter taken along line 19—19 of FIG. 16;

FIG. 20 is a plan view of the divider plate of the proximal manifold ofthe heat exchange catheter shown at 20—20 of FIG. 16;

FIG. 21 is a side view of a heat exchange catheter of the inventionhaving single loop heat exchange elements;

FIG. 22 is a cross-sectional view of the proximal manifold for the heatexchange catheter of FIG. 21;

FIG. 23 is an enlarged cross-sectional view of the distal tip of asingle loop heat exchange element;

FIG. 24 is a cross-sectional view of the proximal shaft portion of theheat exchange catheter taken along line 24—24 of FIG. 21;

FIG. 25 is a plan view of the faceplate of the proximal manifold of theheat exchange catheter taken along line 25—25 of FIG. 22; and

FIG. 26 is a plan view of the divider plate of the proximal manifold ofthe single loop heat exchange catheter taken along line 26—26 of FIG.22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an improved heat exchange catheter thatprovides increased surface area for heat transfer with the respectivebody fluid without increasing the overall cross-sectional size of thecatheter. Although the present invention is primarily intended to beused in the bloodstream for regulating the patient's blood temperature,those of skill in the art well understand that various otherapplications for the catheter of the present invention are possible.Indeed, the present invention may have applications beyond controllingthe temperature of an internal body fluid, and the claims should not beso limited.

In a preferred application, one or more of the catheters of the presentinvention are positioned within a patient's vasculature to exchange heatwith the blood in order to regulate the overall body temperature, or toregulate the temperature of a localized region of the patient's body.The catheter of the present invention may be, for example, suitable forexchanging heat with arterial blood flowing toward the brain to cool thebrain, and may thus prevent damage to brain tissue that might otherwiseresult from a stroke or other injury, or cooling venous blood flowingtoward the heart to cool the myocardium to prevent tissue injury thatmight otherwise occur following an Ml or other similar event.

The heat exchange catheters disclosed herein may be utilized in a heatexchange system suitable for regulating the temperature of a patent or aregion of the patient's body. One example of such a heat exchangecatheter system 20 utilizing any of the catheters disclosed herein isshown in FIG. 1. The system 20 may include a catheter control unit 22and a heat exchange catheter 24 formed with at least one heat transfersection 44. The heat transfer section or sections are located on thatportion of the catheter 24, as illustrated by section 26, that isinserted into the patient. This insertion portion is less than the fulllength of the catheter and extends from the location on the catheterjust inside the patient, when the catheter is fully inserted, to distalend of the catheter. The catheter control unit 22 may include a fluidpump 28 for circulating a heat exchange fluid or medium within thecatheter 24, and a heat exchanger component for heating and/or coolingcirculating fluids within the heat transfer system 20. A reservoir orfluid bag 30 may be connected to the control unit 22 to provide a sourceof heat transfer fluid such as, saline, blood substitute solution, orother biocompatible fluid. A circulatory heat exchange flow channelwithin the catheter may be respectively connected to inlet 32 and outlet34 conduits of the pump 28 for circulation of the heat transfer fluid tocool the flow of fluid within a selected body region. A similararrangement may be implemented for heating of selected body regionssimultaneously or independently from the cooling component of thesystem.

The control unit 22 may further receive data from a variety of sensorswhich may be, for example, solid-state thermocouples to provide feedbackfrom the catheter and various sensors to provide patient temperatureinformation representing core temperature or temperature of selectedorgans or portions of the body. For instance, sensors may include atemperature probe 36 for the brain or head region, a rectal temperatureprobe 38, an ear temperature probe 40, an esophageal temperature probe(not shown), a bladder temperature probe (not shown), and the like.

Based upon sensed temperatures and conditions, the control unit 22 maydirect the heating or cooling of the catheter in response. The controlunit 22 may activate a heat exchanger at a first sensed temperature, andmay also de-activate the heat exchanger at a second sensed temperaturewhich may be relatively higher or lower than the first sensedtemperature or any other predetermined temperature. The control unit 22may of course independently heat or cool selected heat transfer sectionsto attain desired or preselected temperatures in body regions. Likewise,the controller 22 may activate more than one heat exchanger to controltemperature at particular regions of the patient's body. The controllermight also activate or de-activate other apparatus, for example externalheating blankets or the like, in response to sensed temperatures. Theregulation exercised over the heat transfer catheters or other devicesmay be a simple on-off control, or may be a significantly moresophisticated control scheme including regulating the degree of heatingor cooling, ramp rates of heating or cooling, proportional control asthe temperature of the heat exchange region or patient approaches atarget temperature, or the like.

The catheter control unit 22 may further include a thermoelectric coolerand heater (and associated flow conduits) that are selectively activatedto perform both heating and cooling functions with the same or differentheat transfer mediums within the closed-loop catheter system. Forexample, a first heat transfer section 42 located on the insertionportion 26 of at least one temperature regulating catheter 24 maycirculate a cold solution in the immediate head region, oralternatively, within a carotid artery or other blood vessel leading tothe brain. The head temperature may be locally monitored withtemperature sensors 36 positioned in a relatively proximate exteriorsurface of the patient or within selected body regions. Another heattransfer section 44 of the catheter 24 also located on the insertionportion 26 may circulate a heated solution within a collapsible balloonor otherwise provide heat to other body locations through heat elementsor other mechanisms described in accordance with other aspects of theinvention. While heat exchange catheter 24 may provide regionalhypothermia to the brain region for neuroprotective benefits, otherparts of the body may be kept relatively warm so that adverse sideeffects such as discomfort, shivering, blood coagulopathies, immunedeficiencies, and the like, may be avoided or minimized. Warming of thebody generally below the neck may be further achieved by insulating orwrapping the lower body in a heating pad or blanket 46 while the headregion above the neck is cool. It should be understood of course thatmultiple heat exchange sections of the catheter 24 may be modified toprovide whole body cooling or warming to affect body core temperature.

FIG. 2 illustrates one particular heat exchange catheter 50 of thepresent invention inserted into a body cavity, in this case a bloodvessel BV. The blood flow F is indicated by the arrows directed to theright. The heat exchange catheter 50 includes an elongate shaft 52adapted to extend through a puncture wound 54 into the blood vessel BV.The catheter 50 has a proximal end that remains outside the body and adistal end that is inserted into the body cavity.

A heat exchange region 56 is provided along a distal portion of thecatheter 50 which is immersed in the bloodstream. The heat exchangeregion 56 corresponds to either of the heat exchange regions 42 or 44described above with respect to FIG. 1. The illustrated embodiment isshown in more detail in FIGS. 3-6, and includes a plurality of heatexchange elements 58 attached to the catheter shaft 52 providingenhanced heat exchange with the blood, as will be described. Any of theother embodiments disclosed in the present application may besubstituted in the heat exchange region 56.

With reference to FIG. 3, the heat exchange catheter 50 comprises theaforementioned elongate shaft 52 having a heat exchange region 56 on adistal end, and being provided with a plurality of ports 60 on aproximal end. In particular, the catheter 50 includes a fluid inlet port60 a, a fluid outlet port 60 b, and a guide wire insertion port 60 c.

FIG. 4A illustrates a cross-section of the elongate shaft 52 taken alongthe line 4A—4A in FIG. 3, wherein three lumen are provided within theshaft. A guide wire lumen 62 is located generally between two heattransfer fluid circulation lumen 64 and 66. One circulation lumen 64 isin fluid communication with the fluid inlet port 60 a, and the othercirculation lumen 66 is in fluid communication with the fluid outletport 60 b. It may be readily determined, however, that if flow in theopposite direction is desired, for example to achieve counter-currentflow with the blood as described below, either lumen may function asinflow lumen with the other lumen functioning as the outflow lumen. Thedirection of flow may thus be easily and satisfactorily reversed.

FIG. 4B illustrates an alternative cross-section of the elongate shaft52 wherein a centrally disposed guide wire lumen 62′ is located betweentwo heat transfer fluid circulation lumen 64′ and 66′.

The cross-sectional configuration of the shaft 52 desirably extends froma junction with a hub 68 to the distal end 69 of the catheter.Alternatively, the extreme distal portion may consist of just the guidewire lumen or an extension thereof. The view in FIG. 3 is somewhatabbreviated as indicated by the break lines, and the catheter 50 of thisembodiment may be anywhere from 60 to 150 cm in length.

The heat exchange region 56 begins at an outlet manifold 70 and ends atan inlet manifold 72 disposed distally therefrom. A plurality of theaforementioned heat exchange elements 58 extend adjacent to andgenerally in parallel with the shaft 52 between the inlet and outletmanifolds 70, 72. Each element 58 is attached on at least one of itsends to the heat exchange region 56 and at least a portion of its lengthis transversely spaced from the shaft 52 so that when inserted in afluid body cavity having body fluid therein, the body fluidcircumferentially surrounds each heat exchange element. The term“circumferentially surrounds” is not meant to imply that thecross-section of each heat exchange element 58 is circular, but insteadmeans that when viewed in transverse cross-section, each element isperipherally surrounded by body fluid. This greatly increases theeffective heat transfer surface area of the catheter 50 and facilitatesheat exchange with the body fluid.

As seen in cross-section in FIG. 5A, there are six such heat exchangeelements 58 distributed uniformly around the circumference of thecatheter shaft 52. As will be appreciated from the following discussion,improved heat exchange using the catheter 50 of the present inventioncan be accomplished with as few as two heat exchange elements 58. Forexample, FIG. 5B illustrates an alternative embodiment with three heatexchange elements 58′. As illustrated, the heat exchange elements 58 aredistributed evenly around the circumference of the shaft 52, but otherconfigurations such as that shown in FIG. 8 are possible.

The heat exchange catheter 50 of the present invention provides acirculatory fluid flow path therein, as best seen in FIG. 6. In theillustrated embodiment, the circulatory fluid flow path extends throughthe elongated heat exchange elements 58. In FIG. 6, the upper lumen 64functions as a heat exchange medium inflow lumen. The lower lumen 66functions as a heat exchange medium outflow lumen. If the direction ofheat transfer fluid flow in the heat exchange elements is desired to bein the opposite direction from that illustrated here, however, it may bereadily accomplished by reversing the function of these two lumen.

The circulatory flow path in the heat exchange region 56 of the catheter50 is illustrated in FIG. 6 by the flow arrows 74 and 75. Specifically,the exchange medium travels distally through the inflow lumen 64 untilit reaches a port 76 which is in fluid communication with an interiorspace 78 defined within the inlet manifold 72. Each of the heat exchangeelements 58 is desirably formed as a hollow tube having an infloworifice 80 in fluid communication with the interior space 78. In likemanner, each heat exchange element 58 has an outflow orifice 82 that isin fluid communication with an interior space 84 defined within theoutlet manifold 70. The outflow lumen 66 has a port 86 that receivesheat exchange medium exiting from the outflow orifices 82. A plug member88 provided in the outflow lumen 66 prevents heat exchange medium fromcontinuing distally past the outlet manifold 70, while plug members 89close the distal ends of lumen 64 and 66. To reiterate the circulatoryflow path, heat exchange medium travels distally (arrow 74) throughinflow lumen 64 to exit through the port 76, enters the space 78 withinthe inlet manifold 72, travels within the space to enter the infloworifices 80 of each of the heat exchange elements 58, travels proximally(arrows 75) through the heat exchange elements, flows from the outfloworifices 82 into the space 84 formed within the outlet manifold 70, andenters the outflow lumen 66 through the port 86 which carries the mediumback to the proximal end of catheter 50. Again, the heat transfer fluidflow through the heat exchange elements 58 could be in the distal orproximal direction and, depending on the catheter insertion technique,the flow could be con-current or counter-current to the blood flowdirection.

The inlet and outlet manifolds 70, 72 may be formed by a variety ofconstructions, a flared, thin-walled jacket being shown. The manifolds70, 72 transition on one end to meet the exterior of the shaft 52, andare sealed thereto. On the opposite end, the open area within eachmanifold receives the ends of the heat exchange elements 58, and apotting compound 90 which may be a suitable adhesive, seals the interiorspaces 78 and 84 from the exterior of the circulatory flow path. Theheat exchange elements 58 are thus sealed between the respectivemanifolds 70, 72 and the potting compound in a fluid tight manner. Ofcourse, other constructions such as a molded polymer or shrink-wrapmaterial may be substituted for the flared jacket, and otherconstructions such as a sealing ring may be substituted for the pottingcompound.

The heat exchange elements 58 are illustrated as being bowed outwardslightly from the catheter shaft 52. This arrangement ensures that theelements 58 are surrounded by body fluid during use, such as seen inFIG. 2, so as to greatly enhance heat transfer capacity for a givenfluid flow rate. That is, the heat exchange medium is divided at thedistal end of the catheter and flows proximally through a plurality ofparallel paths, each of which passes through heat exchange elements 58each having a continuous external surface. This arrangement is bestillustrated in FIGS. 5A and 5B. In addition, some heat exchange takesplace between the inflow lumen 64 and the external body fluid, throughthe wall of the shaft 52.

One means of ensuring separation between heat exchange elements 58 andshaft 52 is to provide a spring member therebetween, such as that shownat 92 in FIG. 6. A spring member 92 is desirably connected to a radiallyinner portion of each heat exchange element 58 and is cantileveredtoward and into contact with the shaft 52. During insertion of thecatheter 50, external forces may cause the heat exchange elements 58 tobe pressed inward, compressing the spring member 92 which slides againstthe shaft 52. Upon placement in the appropriate body cavity, the springmember 92 expands to move the heat exchange elements 58 radially outwardinto optimum heat exchange position. Advantageously, the spring members92 have a relatively low profile in the blood flow path, and thusminimize any obstruction to blood flow.

Another construction that would assure separation in use between theheat exchange elements 58 and shaft 52 is to provide thin-walled,inflatable tubes as the heat exchange elements. The elements areslightly longer than the distance between the inlet and outletmanifolds, 70, 72. When the elements 58 are collapsed, for example uponinsertion into the patient, they will fold down flat against the shaftto provide a low profile. When they are inflated, for example bypressurized and flowing heat exchange fluid in use, they will bow outaway from the shaft. See, for example, FIG. 3 and FIG. 8. Alternatively,the distance between the inlet and outlet manifolds 70, 72 may bevariable via a pull-wire (not shown) or other such expedient that actson the shaft 52. For example, the shaft 52 may be constructed intelescoping sections, or may be bendable, so that the distance betweenthe inlet and outlet manifolds 70, 72 can be shortened upon actuation ofthe pull-wire. In this manner, the elements 58 initially lie flatagainst the elongated shaft 52 but are then caused to bow outward awayfrom the shortened shaft.

Another advantage of providing a plurality of flexible heat exchangeelements, such as shown at 58, is that the cross-sectional profile ofthe heat exchange region 56 easily conforms to tortuous body cavities.That is, as best seen in FIG. 5A, the circumferential gaps providedbetween each of the individual heat exchange elements 58 permits them toshift radially and circumferentially so that they may be more bunched onone side or the other. This capacity to shift position greatly enhancesthe ability of placing heat exchange region 56 into tight or tortuousbody cavities and in activating the flow of heat exchange fluid toexpand the heat exchange elements without undue restriction of bloodflow around the heat exchange region. It has been found that adequateflow in the blood vessel may generally be retained if the heat exchangeelements obstruct 50% or less of the cross-sectional area of the vessel.

An alternative embodiment of a heat exchange catheter 100 of the presentinvention is seen in FIG. 7. The catheter 100 is similar to the catheter50 described previously in that a heat exchange medium circulation pathis provided therein, and a plurality of elongated heat exchange elements102, discrete from a catheter shaft 104, form a portion of thecirculation path. In the embodiment of FIG. 7, however, the heatexchange region 106 extends along the entire length of the cathetershaft 104.

Each of the heat exchange elements 102 is preferably formed as anelongate hollow filament. The heat exchange catheter 100 includes afluid circulation path therein comprising an inner lumen or lumen 108formed within the inner shaft 104, a space 110 formed within a manifold112 provided at the distal end of the catheter, and the hollow lumen ofthe heat exchange elements 102 are in fluid communication with thatspace 110. The proximal end of the inner shaft 104 fits within an inletfitting 114 having an inner chamber 116 that communicates with the lumen108. The inner shaft 104 extends through a chamber 118 formed in anoutlet fitting 120, and the proximal ends of the heat exchange elements102 are sealed in the fluid communication with the chamber 118 usingpotting compound 122. In this manner, fluid entering the chamber 116, asindicated with arrow 124, is directed into the lumen 108 and travelsdistally through the catheter 100 as indicated by arrows 126. At thedistal manifold 112, the fluid is redirected 180 degrees into the hollowlumen of the heat exchange elements 102. Again, potting compound 128 isused seal the distal ends of the elements 102 within the space 110. Thefluid travels proximally through the elements 102, as indicated byarrows 130, and exits the heat exchange elements into the chamber 118 tobe removed from the chamber as indicated by arrow 132.

The advantage of providing a heat-exchange region 106 along the entirelength of catheter 100 is the capacity for greater heat exchange withthe body fluid. In addition, the catheter 100 having a heat exchangeregion 106 along 100 percent of its length may more effectively providewhole body heating or cooling. Furthermore, in the previously describedcatheter, some heat might be transferred to or from the body fluidthrough the proximal portion of the catheter that is not part of theheat-exchange region. In the embodiment of FIG. 7, on the other hand,the entire catheter is designed to exchange heat with the body fluid.

FIG. 8 illustrates a further embodiment of a heat exchange catheter 150having a heat exchange region 152 on its distal portion, and aninsulating region 154 on its proximal portion. In the illustratedembodiment, the heat exchange region 152 and insulating region 154 areapproximately equal in length, both being about 50 percent of the entirelength of the catheter 150. In a preferred embodiment, the insulatingregion 154 is substantially longer than the heat exchange region 152,and preferably at least 75 percent of the length of the catheter 150.Desirably, the combined length of the heat exchange region 152 andinsulating region 154 is approximately equal to the entire length of thecatheter 100. One specific example is an insulating region that extendsabout 85-90% of the total catheter length, and a heat exchange regionthat extends the remaining 10-15%. Of course, various alternativeconfigurations are contemplated, including intermittent and interspersedinsulating and heat exchange regions.

As before, the catheter 150 in FIG. 8 includes a heat exchange mediuminlet port 160 and a heat exchange medium outlet port 162. A fluidcirculation path (not shown) is provided within an elongate shaft 164. Aplurality of elongated heat exchange elements 166 are provided parallelto but spaced from the shaft 164 in the heat exchange region 152.Preferably, the heat exchange elements 166 are hollow filaments thatform separate parts of the fluid circulation path within the catheter150. To this end, a distal manifold 168 receives the distal ends of theheat exchange elements 166, and a proximal manifold 170 receives theproximal ends. The manifolds 168,170 define fluid flow spaces therein; aspace within the distal manifold 168 being in fluid communication withthe inlet port 160, and a space within the proximal manifold 170 beingin fluid communication with the outlet port 162. In this manner, aliquid heat exchange medium flows into the port 160 and to the distalend of the catheter 150 before returning to the outlet port 162 via thehollow heat exchange elements 166.

The insulating region 154 includes an insulating member 172 disposedlongitudinally about the shaft 164. The insulating member 172 may be avariety of constructions, including a solid sleeve or a fluid-filledballoon. In a preferred embodiment, the insulating member 172 comprisesan inflatable balloon having an interior space in communication with aninflation port 173. A suitable insulating fluid, such as nitrogen gas orcarbon dioxide gas, inflates the balloon 172 away from the side of theshaft 164. In this manner, even if the entire length of the shaft 164 isimmersed in a body fluid, only the heat exchange region 152 transfersheat efficiently to or from the body fluid.

As seen in FIG. 8A, the shaft 164 may be centered within and held spacedfrom the insulating member 172, for example by collapsible stand-offs175, to prevent the shaft from resting against the side of the inflatedinsulating member and comprising the insulating capacity of theinsulating member. The stand-offs 175 may be relatively thin andflexible so that when the insulating member is collapsed for insertionand removal, they fold down against the shaft without addingsignificantly to the overall catheter profile.

Alternatively, as shown in FIG. 8B, the insulating member could be amulti-lumen, thin-walled balloon with a central lumen into which theshaft 164 is inserted, and inflatable insulating lumens 179 surroundingthe central lumen. An insulating sleeve 181 may surround the entireinsulating region.

The configuration of FIG. 8 having an insulating region and a heattransfer region may be particularly useful in cooling blood flowing tothe brain to regionally direct the cooling effect of the catheter. Theeffectiveness of cooling or heating the blood depends in part upon thedifference in temperature between the surface of the heat exchangeregion in contact with the blood, and the temperature of the blood. Thisdifference in temperature is referred to herein as ΔT. The catheter 150can be inserted in, for example the femoral artery, passed through thevasculature, for example up the aorta, so that the heat exchange region152 is located in the carotid artery. The heat exchange fluid iscirculated through the catheter 150, and remains cool until it reachesthe heat exchange region 152 by virtue of the insulating region 154, andthus a maximum ΔT is maintained. Without the insulating region 154, theeffectiveness of the heat exchange medium is diminished, andsignificantly less cooling of the blood at the desired location, in thiscase the carotid artery, may result.

Additionally, the regional effect of the cooling may also be compromisedby the exchange of heat with blood that does not subsequently circulateto the desired region of the body. In the example above of regionallycooling the brain, the insulating region 154 prevents the cold heatexchange fluid from exchanging heat with the blood within the arterialsystem in the femoral artery and the ascending aorta, which blood wouldcirculate to the trunk and legs of the patient. This cooling of bloodwhich then circulates to other regions of the body can result in ageneral cooling of the entire body. While this general cooling may bedesirable in some applications, it may be undesirable in otherapplications such as applications wherein it is intended to effectregional or localized cooling of the heart or the brain. In this regard,such general cooling can result in discomfort, such as shivering, in thepatient, or other negative side effects of whole body hypothermia thatmight be avoided by regional cooling.

Up to now, the heat exchange elements have been described as hollowfilaments forming a portion of a fluid flow path and attached at bothends to the catheter shaft. The present invention is of a more generalnature, however, in that the multiple and distinct heat exchangeelements need not be attached at both ends to the shaft, but may insteadbe constrained along a portion of its length with respect to the shaftso that a free end thereof is permitted to drift freely within the bodyfluid. The freely floating elements desirably define an internal“cul-de-sac” fluid flow path.

In particular, FIG. 9 illustrates a heat exchange catheter 180 inaccordance with the present invention having an elongate shaft 182 and aplurality of heat exchange elements 184 attached thereto. The heatexchange elements 184 are attached at distal ends to the shaft 182 andare generally free-floating at distal tips 186. These elements 184 arepreferably flexible and collapsible so as to compress against theexterior of the shaft 182 to provide a low profile during insertion andremoval of catheter 180. In addition, the flexible nature of theelements 184 facilitates location in and passage through tortuouspassages, and minimization of restriction to flow of blood through thevessels when inflated. It should be noted that the elements 184 alongany one catheter 180 may be of different lengths. The catheter 180further may include a proximal insulating member 188, which may be asingle- or multi-lumen balloon as described above.

The heat exchange elements 184 can be provided in the variety ofconstructions. Each of the heat-exchange elements 184 may provide fluidcirculation therein. The cross-sectional view of FIG. 9A illustrates theheat exchange element 184 having a fluid inlet path 190 and a parallelfluid outlet path 192. The fluid paths 190,192 are placed in fluidcommunication with a main circulation path provided within the shaft182. In this manner, the heat exchange elements 184 are somewhat similarto the elements 58 described above with respect to the first embodiment,but are somewhat freer to float within the body fluid. In addition, theelements 184 being attached at only one end permits them to more freelymigrate around circumference of the shaft 182 when the catheter 180 isadvanced through tortuous passage ways. A further embodiment of thisnature is seen in FIGS. 13 and 14.

To further facilitate heat exchange between the body fluid and the heatexchange elements described herein, each of the elements may be providedwith a flow disrupting rib or other discontinuity. It is a well-knownprinciple of heat exchange that reducing the laminar boundary layeraround an object in a fluid flow path increases the potential heattransfer between that object and the fluid. Thus, for example, FIG. 10Aillustrates a tubular heat exchange element 200 provided with a helicalrib 202 thereon. Other such configurations are possible, includingcircumferentially oriented ribs 204 on a heat exchange element 206, asseen in FIG. 10B.

To still further facilitate heat transfer between the exchange elementsand a body fluid, the surface area of those elements can be increased inseveral ways without significantly altering the overall cross-sectionalvolume of the catheter. Thus, for example, FIG. 11 illustrates a heatexchange region 210 on a catheter of the present invention wherein aplurality of undulating heat exchange elements 212 extend from a distalmanifold 214 to a proximal manifold 216 provided on a shaft 218. Statedanother way, the elements 212 extend in a non-linear path with at leastone point of inflection. This configuration provides greater surfacearea for each heat exchange element 212 than the shallow convexity ofelements 58, 102, and 166, previously described. Furthermore, the factthat each element 212 is located generally parallel to but spaced fromthe main shaft 218 permits them to compress inward and/or migrate aroundthe circumference of the shaft when passing the catheter through narrowor tortuous body cavities.

Another means for increasing the surface area of each heat exchangeelements is to modify their cross-section from a purely circularcross-sectional geometry. Thus, FIG. 12 illustrates, in cross-section, aheat exchange element 220 having a plurality of alternating outwardlyprojecting regions 222 and grooves 224. The overall cross-sectionalfootprint, if you will, fits within an imaginary circle 226, but has agreater exterior surface area. Those of skill in the art will recognizethat numerous cross-sectional configurations for the heat exchangeelements satisfying the dual requirements of an increased surface areawithout increasing the overall cross-sectional footprint are possible.

An alternative construction for the heat exchange elements is shown inFIGS. 13 and 14. A catheter shaft 240 contains an inlet fluid flow lumen242 and an outlet fluid flow lumen 244. A plurality of heat exchangeelements 246 attach at only one end along the length of the shaft 240 sothat they may float freely in surrounding body fluid. Each heat exchangeelement 246 comprises an outer tubule 248 surrounding an inner tubule250. The distal end of the outer tubule 248 is closed and the distal endof the inner tubule 250 is open and terminates short of the distal endof the outer tubule. The inner tubules 250 define lumen therein that arein fluid communication with the inlet lumen 242. In addition, the outletlumen 244 is in fluid communication with the annular space between theinner tubule 250 and outer tubule 248. In this manner, heat transferfluid traveling through the inlet lumen 242 of the shaft of the catheterenters the inlet tubule lumen, as indicated by arrows 252, and flowsbetween the inner and outer tubules and into the outlet lumen 244 of theshaft, as indicated by arrows 254. The heat exchange medium circulationpath in this case includes so-called cul-de-sac heat exchange elements.The outer surface of the outlet tubule is surrounded by body fluid, forexample blood, and as heat transfer fluid circulates through thetubules, heat may be transferred between the heat transfer fluid and thebody fluid. It should be noted that the direction of fluid flow could bereversed, and the flow structure need not be precisely as illustrated.For example, the inlet and outlet lumen in the shaft need not beconcentric, other configurations are possible.

A still further alternative construction for the heat exchange elementsis shown in FIGS. 15-20. This embodiment includes a proximal manifold300 and a plurality of heat exchange elements 302, wherein proximalportions of the individual heat exchange elements 302 are bundled orpositioned within a shaft or sleeve 306. Distal portions of the heatexchange elements 302 protrude out of and freely extend beyond thedistal end of the sleeve 306.

With particular reference to FIG. 15, the catheter includes a guidewiretube 304 that extends through the proximal manifold 300 and beyond thedistal ends of the heat exchange elements 302. The sleeve 306 maycomprise a flexible tubular structure that substantially surrounds themultiple heat exchange elements 302 (that comprise flexible tubes) andthe guidewire tube 304, along substantially the entire length of thecatheter. The portions of the heat exchange elements that protrudebeyond the distal end of the sleeve 304 define the heat exchange regionof this particular embodiment of the invention. Optionally, the tubularsleeve 306 may be flared at a proximal end 308 to facilitate convergenceof the multiple heat exchange elements 302 into a single, low-profiletube.

The heat exchange elements 302 are unconstrained and float freely withthe body fluid beyond a distal end 310 of the tubular sleeve 306. Theembodiment illustrated shows eight heat exchange elements 302, althoughother numbers are possible. The guidewire tube 304 is generally stifferthan the heat exchange elements 302. A temporary attachment means (notshown) may initially be provided to couple the loose portions of theheat exchange elements 302 and the guidewire tube 304 or a temporaryadhesive releasably attaching the heat exchange elements to theguidewire tube. Such attachment means may be in the form of anelastomeric band around all of the heat exchange elements 302 and theguidewire tube 304. Such a weak, temporary attachment may be overcomewhen the elements 302 are inflated during operation of the catheter, ormay be severed by other suitable means.

As seen in the detailed view of FIG. 17 and cross-section of FIG. 18,the heat exchange elements 302 comprise coaxial tubes, each having aninner lumen 312 and an outer lumen 314. At the distal end 316 of each ofthe elements 302, the outer lumen 314 is closed, and the inner lumenterminates short of this distal end. The flow arrows show heat exchangemedium passing distally through the inner lumen 312, and beingredirected at the distal end 316 to travel proximally through the outerlumen 314.

As seen in FIG. 16, the proximal manifold 300 comprises a containergenerally divided into two equal chambers; an inlet chamber 318, and anoutlet chamber 320. The inlet chamber 318 has a fluid inlet port 322,and the outlet chamber 320 has a fluid outlet port 324. The two chambers318, 320 are separated by a divider plate 326. Each of the heat exchangeelements 302 passes through a front plate 328 of the manifold 300.

As seen in FIGS. 16 and 17, the inner lumen 312 are defined within inputtubes 330 terminating in the inlet chamber 318. Likewise, the outerlumen 314 are defined within output tubes 332 terminating in the outletchamber 320. The input and output tubes 330, 332 pass through holes 334formed in the front plate 328, as seen in FIG. 19. Each of the holes 334fluidly seals around the tubes 330, 332. A central hole 335 for passageof the guidewire tube 304 is also provided in the front plate 328. Theguidewire tube 304 extends in a sealed manner through the central hole335. With reference to FIG. 20, the divider plate 326 includes a centralhole 338 fluidly sealed around the guidewire tube 304. The guidewiretube 304 continues through a single hole 340 provided in the back plateof the manifold 300. Each input tube 330 passes through a hole 336 inthe divider plate 326, and is fluidly sealed with respect thereto.

In use, the catheter is inserted into a blood vessel and heat exchangefluid is introduced through the inlet port 322 and into the inflowchamber 318. The heat exchange fluid then passes into the open proximalends of each of the inlet tubes 330, and into the inner lumen 312 ofeach of the heat exchange elements 302. The fluid passes along thelength of each of the heat exchange elements 302 until it is re-directedat the distal end 316 into the outer lumen 314. The fluid then travelsproximally through the outer lumen 314, as seen FIG. 17, until itreaches the open proximal ends of each of the outlet tubes 332. If theheat exchange elements 302 are initially in a collapsed configuration,the flow of heat exchange fluid inflates them and may cause severance ofan attachment means and subsequent separation of each of the elements.The fluid ultimately passes into the outlet chamber 320 and exits themanifold 300 through the outlet port 324. In this manner, heat exchangefluid may be circulated through the heat exchange catheter. As the heatexchange fluid returns proximally through the outer lumen 314, itexchanges heat with blood flowing past the surface of the elementsthrough the outer wall of the heat exchange elements 302.

While the example given shows fluid circulating distally through theinner lumen 312, and proximally through the outer lumen 314, those ofskill in the art will appreciate that the direction of flow maysometimes be reversed by merely introducing heat exchange fluid into theinlet chamber, while removing it from the outlet chamber. It isgenerally desirable to have counter-current heat exchange, that is, thatthe blood flow is in the opposite direction to the flow of the heatexchange fluid in the outer lumen 314. If the heat exchange elements 302are in the bloodstream such that the distal ends of the elements aredownstream, and blood is flowing from proximal to distal along thesurface of the catheter, the inlet flow of heat exchange fluid isdesirably through the inner lumen 312 and the outlet flow is desirablythrough the outer lumen 314. This flow arrangement is preferred for thecatheterwith free-floating heat exchange elements on the distal end,because even if the blood flows distal to proximal, the elements tend toprolapse and float backward toward the proximal end of the catheter. Insuch a configuration, counter flow is achieved if the heat exchangefluid is flowing back out of the catheter through the outer lumen 314.

With reference now to an alternative embodiment shown in FIGS. 26-31, aheat exchange catheter 350 of the present invention includes a pluralityof heat exchange elements that are formed of a loop of single lumentubing that extends the entire length of the catheter. The inlet end ofeach of the single lumen tubes is open to an inlet reservoir of amanifold, and the outlet end is open to the outlet reservoir. Heatexchange fluid circulates along the entire length of each of the heatexchange elements.

Referring particularly to FIG. 21, a single loop heat exchange catheter350 comprises a proximal manifold 352, a plurality of coaxial heatexchange elements 354, a guidewire tube 356, and a proximal tubularsleeve 358 that surrounds the heat exchange elements in the proximalregion of catheter. The catheter 350 illustrated shows eight such heatexchange elements 354, each comprising loops of long single lumen tubes.Of course, those of skill in the art will understand that the number ofheat exchange elements may be varied. The proximal end 360 of thetubular sleeve 358 may be flared to facilitate a convergence of a themultiple heat exchange elements 354 into a single, lower profile tube.

At the distal end 362 of the sleeve, the heat exchange elements 354 areunconstrained and may float freely. The guide wire tube 356 is generallystiffer than the heat exchange elements 354, and a loose attachment (notshown) may temporarily be formed therebetween. For example, anattachment means such as elastomeric band around all of the heatexchange elements 354 and the guidewire tube 356 may be used.Alternatively, any weak, temporary attachment means that can be overcomewhen the elements 354 are inflated can be substituted.

As seen in FIG. 22, the proximal manifold 352 defines within tworeservoirs; an inflow reservoir 368 an outflow reservoir 370. A dividerplate 372 separates the two reservoirs 368, 370. An inflow port 374communicates with the inflow reservoir 368, while on outflow port 376communicates with the outflow reservoir 370. A front plate 378 forms thefront surface of the manifold 352, as seen in plan view in FIG. 25.

The heat exchange elements 354 comprise long, thin-walled tubes, eachdefining a single lumen 364 therein. Each tube has an open end 366positioned in the inflow reservoir 368 and extends distally throughsealed apertures 380 in the divider plate 372 (FIG. 26). The tubes passthrough the outflow reservoir 370 and through sealed apertures 382 inthe front plate 378 (FIG. 25). The tubes continue distally, convergingin the flared portion 360 of the tubular sleeve 358, and emerging from adistal end 362. Each of the heat exchange elements 354 extends for somedistance to a distal bend 384, seen in FIG. 23. The distal flow of heatexchange fluid is thus re-directed proximally at the distal bend 384.The return tube again passes through one of the apertures 382 in thefront plate 378, and terminates in the outflow reservoir 370.

A guidewire tube 356 passes entirely through the manifold 352, extendingthrough a proximal guidewire hole 388, a central aperture 390 in thedivider plate 372, and a central aperture 392 in the front plate 378.The guidewire tube 356 is sealed from both reservoirs 368,370 in themanifold 352.

In use, heat transfer fluid (represented by the arrows in the variousFIGURES) is introduced into the inflow reservoir 368 through the inflowport 374. The pressurized fluid passes into the open ends of each of theheat exchange element tubes 354, flows the entire length of the tube andis redirected at the bend 384, and then flows proximally, emptying intothe outflow reservoir 370. The fluid is then exhausted through theoutlet port 376. As previously stated, those of skill in the art willunderstand that the direction of flow may be easily reversed withoutaltering the basic principles of the invention. In this embodiment,however, the heat exchange fluid will be flowing in both directions in atube in contact with the blood flow, and therefore both co- andcounter-current flow will exist. Thus, the direction of flow through thetubes becomes less significant than in the coaxial arrangement describedabove.

The heat exchange elements of the present invention may be formed from avariety of materials, the main consideration being biocompatibility. Theelements are fluid impermeable, preferably some form of polymer, andflexible. One particularly useful material is polyethylene terephthalate(PET) which can be extruded and blown to form thin-walled hollowfilaments.

While a particular embodiment of the invention has been described above,for purposes of or illustration, it will be evident to those skilled inthe art that numerous variations of the details may be made withoutdeparting from the invention as defined in the appended claims. By wayof example and not limitation, where heat is exchanged between twoflowing fluids, as between the flowing heat exchange fluid in thiscatheter and flowing blood, it has been found that the heat exchange ifmore efficient if there is counter-current flow between the fluids, thatis that the fluids are flowing in opposite directions. In the examplegiven here, the blood may be flowing past the heat exchange filamentsfrom proximal to distal or from distal to proximal depending on themeans of inserting the catheter. For example, if the catheter isinserted into the inferior vena cava through a jugular vein incision,the blood would flow over the heat exchange region from the distal endtoward the proximal end of the catheter (i.e., retrograde flow), whereasif the catheter is inserted into the inferior vena cava from a femoralvein incision, the blood would flow past the heat exchange region fromproximal toward distal (i.e., antegrade flow). In order to achievecounter-current flow between the blood and the heat exchange fluid, theinlet and outlet lumen of the shaft may be reversed without departingfrom the invention as described. Similarly other variations of theembodiments described are anticipated within the scope of the inventionas claimed.

What is claimed is:
 1. A heat exchange catheter comprising: alongitudinal catheter shaft with a proximal end and a distal end; a heatexchange region comprising a plurality of heat exchange elements, eachof said heat exchange elements having a length and opposed ends and eachof said heat exchange elements being disposed such that, when the heatexchange region of the catheter is positioned in a body lumen or bodycavity that contains body fluid, the body fluid may circumferentiallysurround at least a portion of each heat exchange element, furtherincluding an insulating region on the shaft located proximally withrespect to the heat exchange region and wherein the insulating regioncomprises an inflatable balloon surrounding the shaft.
 2. The catheterof claim 1, wherein at least some of the heat exchange elements have afluid flow path therethrough.
 3. The catheter of claim 2, wherein atleast some of the heat exchange elements have a non-circularcross-section.
 4. The catheter of claim 2, wherein the shaft has a fluidinflow lumen and a fluid outflow lumen and a circulation pathwaytherebetween for the circulation of heat exchange medium, at least someof the heat exchange elements being in the circulation pathway to enablecirculation of a fluid heat exchange medium through the heat exchangeelements.
 5. The catheter of claim 4, wherein each heat exchange elementhas an inflow orifice on one end and an outflow orifice on the opposedend, the inflow orifice and the outflow orifice being in communicationwith the circulation pathway.
 6. The catheter of claim 5, wherein eachheat exchange element extends in a non-linear path from its infloworifice to its outflow orifice, the non-linear path having a least onepoint of inflection.
 7. The catheter of claim 5, wherein the catheterincludes an inlet manifold open to the inflow lumen and to the infloworifice of each heat exchange element, and the catheter includes anoutlet manifold open to the outflow lumen and to the outflow orifice ofeach heat exchange element.
 8. The catheter of claim 7, wherein theinlet manifold is disposed distally with respect to the outlet manifold.9. The catheter of claim 7, wherein the heat exchange elements compriseelongate hollow filaments having opposed open ends defining therespective inflow and outflow orifices, and wherein each filament openend communicates with an interior space in a respective manifold. 10.The catheter of claim 7 wherein the heat exchange elements are longerthan the distance between the inlet and outlet manifold.
 11. Thecatheter of claim 1, wherein the shaft has a length and the heatexchange region extends a distance that is less than one half the lengthof the shaft.
 12. The catheter of claim 11, wherein the heat exchangeregion is located on the distal region of the shaft.
 13. The catheter ofclaim 1, wherein the insulating region extends the entire length of theshaft proximal of the heat exchange region.
 14. The catheter of claim 1,wherein the insulating region extends approximately 85-90% of the lengthof the shaft, and a heat exchange region extends substantially along therest of the shaft.
 15. The catheter of claim 1, wherein the shaft iswithin the balloon and the insulating region comprises a plurality ofstand-offs interposed between and spacing apart the inner wall of theballoon and the shaft.
 16. The catheter of claim 1, wherein theinsulating region comprises a plurality of the balloons surrounding theshaft and a sleeve encompassing the balloons.
 17. The catheter of claim1, wherein there are at least three heat exchange elements.
 18. Thecatheter of claim 17, wherein the heat exchange elements are evenlycircumferentially distributed about the shaft.
 19. The catheter of claim1 wherein said catheter shaft comprises a plurality of heat exchangeelements substantially surrounded by a sleeve and wherein the heatexchange region comprises portions of the heat exchange elements thatprotrude out of said sleeve.
 20. A heat exchange catheter comprising: alongitudinal catheter shaft with a proximal end and a distal end; a heatexchange region comprising a plurality of heat exchange elements each ofsaid heat exchange elements having a length and opposed ends and each ofsaid heat exchange elements being disposed such that, when the heatexchange region of the catheter is positioned in a body lumen or bodycavity that contains body fluid, the body fluid may circumferentiallysurround at least a portion of each heat exchange element, wherein theheat exchange elements are flexible and each is constrained along aportion of its length with respect to the shaft so that a free end ofeach heat exchange element is permitted to drift freely within the bodyfluid.
 21. The catheter of claim 20, wherein the heat exchange elementscomprise very thin-walled balloons.
 22. The catheter of claim 20,wherein the heat exchange elements have walls permitting a high rate ofconductive heat transfer therethrough.
 23. The catheter of claim 20,wherein the heat exchange elements are hollow, the shaft including afluid circulation path, and the hollow interior of the heat exchangeelements being in fluid communication with the fluid circulation path.24. The catheter of claim 23, wherein each heat exchange element has adistal end and a proximal end, the distal end of each being attached tothe catheter shaft.
 25. The catheter of claim 23, wherein each heatexchange element has a distal end and a proximal end and extends from aproximal end of the catheter shaft to beyond the distal end of thecatheter shaft, the plurality of heat exchange elements being retainedclosely together by the shaft except at their distal ends where they areseparate and permitted to float freely in the body fluid.
 26. Thecatheter of claim 25, further including a proximal manifold forsupplying and removing a heat exchange medium to the hollow interior ofeach heat exchange element.
 27. The catheter of claim 26, wherein eachheat exchange element is formed with a coaxial flow path, the heatexchange medium being supplied to an inner lumen and removed from anouter lumen.
 28. The catheter of claim 26, wherein each heat exchangeelement comprises a loop of a single lumen tube, the heat exchangemedium being supplied to the tube lumen.
 29. The catheter of claim 20,wherein the shaft has a length and the heat exchange region extends adistance that is less than one half the length of the shaft.
 30. Thecatheter of claim 29, Wherein the heat exchange region is located on thedistal region of the shaft.
 31. The catheter of claim 20, furtherincluding an insulating region on the shaft located proximally withrespect to the heat exchange region.
 32. The catheter of claim 31,herein the insulating region comprises an inflatable balloon surroundingthe shaft.
 33. The catheter of claim 32, wherein the shaft is within theballoon and the insulating region comprises a plurality of stand-offsinterposed between and spacing apart the inner wall of the balloon andthe shaft.
 34. A heat exchange catheter comprising: a longitudinalcatheter shaft with a proximal end and a distal end; a heat exchangeregion comprising a plurality of heat exchange elements, each of saidheat exchange elements having a length and opposed ends and each of saidheat exchange elements being disposed such that when the heat exchangeregion of the catheter is positioned in a body lumen or body cavity thatcontains body fluid, the body fluid may circumferentially surround atleast a portion of each heat exchange element, wherein each heatexchange element comprises a filament having a distal end and a proximalend, the distal end being attached to the catheter shaft, and furtherincluding a spring member positioned between the filament and the shaftand adapted to compress upon application of an external force to thecatheter as it is being inserted into the body cavity, and expand in theabsence of such an external force to maintain the filament apredetermined radial distance away from shaft.
 35. The catheter of claim34 wherein each filament is further attached at its proximal end to thecatheter shaft, each filament being hollow and providing a fluid flowpath therethrough for passage of a liquid heat exchange medium.
 36. Thecatheter of claim 35, wherein the shaft has a fluid inflow lumen and afluid outflow lumen and a circulation pathway therebetween for thecirculation of heat exchange medium, at least some of the hollowfilaments being in the circulation pathway.
 37. The catheter of claim36, wherein each hollow filament has an inflow orifice on one end and anoutflow orifice on the opposed end, the inflow orifice and the outfloworifice being in communication with the circulation pathway.
 38. Thecatheter of claim 37, wherein the catheter includes an inlet manifoldopen to the inflow lumen and to the inflow orifice of each hollowfilament, and the catheter includes an outlet manifold open to theoutflow lumen and to the outflow orifice of each hollow filament,wherein the inlet manifold is disposed distally with respect to theoutlet manifold.
 39. The catheter of claim 34, wherein the shaft has alength and the heat exchange region extends a distance that is less thanone half the length of the shaft.
 40. The catheter of claim 39, whereinthe heat exchange region is located on the distal region of the shaft.41. The catheter of claim 34, further including an insulating region onthe shaft located proximally with respect to the heat exchange region.42. The catheter of claim 41, wherein the insulating region comprises aninflatable balloon surrounding the shaft.
 43. The catheter of claim 42,wherein the shaft is within the balloon and the insulating regioncomprises a plurality of stand-offs interposed between and spacing apartthe inner wall of the balloon and the shaft.
 44. A heat exchangecatheter comprising: a longitudinal catheter shaft with a proximal endand a distal end; a heat exchange region comprising a plurality of heatexchange elements, each of said heat exchange elements having a lengthand opposed ends and each of said heat exchange elements being disposedsuch that, when the heat exchange region of the catheter is positionedin a body lumen or body cavity that contains body fluid, the body fluidmay circumferentially surround at least a portion of each heat exchangeelement, wherein each heat exchange element comprises a rod-likefilament having a flow disrupting rib disposed thereon.
 45. The catheterof claim 44, wherein the flow disrupting rib is helically disposed aboutthe filament.
 46. The catheter of claim 44, wherein the flow disruptingrib is circumferentially disposed about the filament.
 47. The catheterof clam 44, wherein at least some of the heat exchange elements have afluid flow path therethrough.
 48. The catheter of claim 47 wherein atleast some of the heat exchange elements have a non-circularcross-section.
 49. The catheter of claim 47, wherein the shaft has afluid inflow lumen and a fluid outflow lumen and a circulation pathwaytherebetween for the circulation of heat exchange medium, at least someof the heat exchange elements being in the circulation pathway to enablecirculation of a fluid heat exchange medium through the heat exchangeelements.
 50. The catheter of claim 49, wherein each heat exchangeelement has an inflow orifice on one end and an outflow orifice on theopposed end, the inflow orifice and the outflow orifice being incommunication with the circulation pathway.
 51. The catheter of claim50, wherein each heat exchange element extends in a non-linear path fromits inflow orifice to its outflow orifice, the non-linear path having aleast one point of inflection.
 52. The catheter of claim 50, wherein thecatheter includes an inlet manifold open to the inflow lumen and to theinflow orifice of each heat exchange element, and the catheter includesan outlet manifold open to the outflow lumen and to the outflow orificeof each heat exchange element.
 53. The catheter of claim 52, wherein theinlet manifold is disposed distally with respect to the outlet manifold.54. The catheter of claim 52, wherein the heat exchange elementscomprise elongate hollow filaments having opposed open ends defining therespective inflow and outflow orifices, and wherein each filament openend communicates with an interior space in a respective manifold. 55.The catheter of claim 52 wherein the heat exchange elements are longerthan the distance between the inlet and outlet manifold.
 56. Thecatheter of claim 44, wherein the shaft has a length and the heatexchange region extends a distance that is less than one half the lengthof the shaft.
 57. The catheter of claim 56, wherein the heat exchangeregion is located on the distal region of the shaft.
 58. The catheter ofclaim 44, further including an insulating region on the shaft locatedproximally with respect to the heat exchange region.
 59. The catheter ofclaim 58, wherein the insulating region extends the entire length of theshaft proximal of the heat exchange region.
 60. The catheter of claim59, wherein the insulating region extends approximately 85-90% of thelength of the shaft, and a heat exchange region extends substantiallyalong the rest of the shaft.
 61. The catheter of claim 58, wherein theinsulating region comprises an inflatable balloon surrounding the shaft.62. The catheter of claim 61, wherein the shaft is within the balloonand the insulating region comprises a plurality of stand-offs interposedbetween and spacing apart the inner wall of the balloon and the shaft.63. The catheter of claim 61, wherein the insulating region comprises aplurality of the balloons surrounding the shaft and a sleeveencompassing the balloons.